1. Technical Field
The present invention relates in general to a multi-level circuit structure for mounting electronic devices thereon. More particularly, the present invention relates to methods for construction of multi-level circuit cards formed from a plurality of substrates having electrically conductive cores. Still more particularly, the present invention relates to methods for construction of multi-level circuit cards formed from a plurality of substrates having electrically conductive cores which permit accurate alignment of each level within the multi-level circuit card.
2. Description of the Related Art
In electronic computers, electronic devices or modules housing electronic devices, are mounted on circuit cards which electrically interconnect the various electronic devices and modules. Multi-layer circuit cards are conventionally manufactured by laminating together a number of substrates, i.e. epoxy-fiberglass, having copper circuitry on each side. The multi-layer laminate is then drilled to form the many interconnections or "vias" which are necessary for interlayer connection. Registration of the cores must be extremely precise because misalignment will lead to an unusable circuit card.
U.S. Pat. No. 3,606,677 describes a multi-layer structure formed by laminating dielectric substrates having conductive patterns thereon with unmetalized substrates therebetween.
U.S. Pat. No. 3,795,047 describes a multi-layer structure which is formed by laminating subassemblies which are electrically interconnected by uniform spherical particulate powder embedded in an epoxy between adjacent layers.
U.S. Pat. No. 4,683,653 describes a multi-layer circuit board which is formed from laminated dielectric base plates with circuit patterns disposed thereon.
U.S. Pat. No. 3,436,819 describes a multi-layer circuit board formed from laminating circuitized dielectric substrates.
U.S. Pat. No. 4,496,793 describes a multi-layer circuit board which includes one or more metal stabilizing sheets for adjusting the thermal coefficient of expansion of the laminate.
U.S. patent application Ser. No. 07/339,384 assigned to the assignee herein discloses a multi-level structure which includes layers which are formed from thermally and/or electrically conductive core materials which are coated with a dielectric material. By utilizing a thermally and/or electrically conductive core each substrate in a multi-level circuit card formed in this manner will have increased structural stability. By forming structures from multiple substrates, each having an enhanced structural stability, the resultant multi-level circuit card will have greatly enhanced structural stability. Additionally, where the core of each substrate is electrically conductive, the core may be used as a ground or power plane, thereby eliminating the need to separately include a conductive layer or sheet as a ground or power plane. A problem which exists with each of the aforementioned prior art structures is the particularly precise registration which is required of each layer during construction so that interconnections which are drilled through multiple layers will intersect the various conductive patterns at precise points.
It should therefore be apparent that a need exists for a multi-level circuit card structure which permits accurate registration of multiple levels within the structure.